A general method of shielding against noise from indoors or outdoors is by shutting it out with walls, doors or windows. Additionally, when noise is generated within a specific area, there are methods of sealing off the relevant area. Methods for doing so include using tightly sealable sashes for doors and windows, giving them a double structure, or using sound-absorbing materials. In any case, this usually necessitates blocking the flow of air between the source of the noise and the area to be soundproofed.
On the other hand, soundproofing methods allowing air flow include those such as the “soundproofed low energy consumption healthy living room system using natural circulation of outdoor air” described in JP 2003-21373 A, wherein box-shaped tubes with air passage holes are provided, these air passage holes are filled with a sound-absorbing material, and the boxes are provided with complicated air flow routes to reduce noise, as well as the “sound insulating material structure and soundproofing structure of an air conditioner” described in JP H10-39875 A, wherein porous through holes are added and a foamed material is used.
Alternatively, there are methods such as mufflers for reducing engine exhaust noise and noise cancellers or silencers for reducing the firing noise of guns. The “internal combustion engine exhaust noise reducing device and exhaust noise tuning method using said device” of JP 2006-250022 A has a gas flow path of at least a certain length and the flow of gas is made complicated to raise the sound insulating effect.
Furthermore, methods of canceling noise by manipulating the acoustic signal of noise, called noise-canceling speakers or noise cancellers, are known. JP 2002-367298 A provides examples of noise canceller devices and noise canceling methods.
In order to improve on the conventional soundproofing technologies mentioned above, the present applicant proposed an improved soundproofing plate for effective reducing transmitted acoustic energy while permitting the flow of air in WO 2012/086680, the entire disclosure of which is hereby incorporated by reference. The proposed soundproofing plate comprises a substrate having a through hole formed therein, and a soundproofing device mounted on the through hole of the substrate. This soundproofing device comprises a sound collecting portion having in the center a through hole (“air passage hole”) communicating with the through hole in the substrate, both ends or one end being of a larger size than the air passage hole of the device, and being arranged so as to reflect incident noise. According to the proposed soundproofing plate, an effective soundproofing effect can be achieved while enabling passage of outside air without consuming artificial energy such as for air conditioning or the like. However, even this proposed soundproofing plate left room for improvement.